1. Field of the Invention
The present invention relates to a cyclone separator having an incorporated coalescer and, more particularly, to such a separator having a coalescer which is adapted to form an upstream pretreatment stage therefor.
2. Description of Related Art
Cyclone separators, more commonly called hydrocyclones, are generally intended for separating two immiscible phases of different densities. In this type of separator, the mixture of the two phases to be separated is injected at high speed into a chamber which is generally cylindrical so that the mixture progresses through the chamber with a gyratory movement. The centrifugal forces generated by this gyratory movement acting on the mixture of two phases of different densities causes the migration of the denser phase towards the wall of the chamber, the lighter phase remaining towards the interior of the chamber. By arranging two axial outlets for the phases, one towards the wall of the chamber and the other along the axis of the chamber, and by using a back-pressure arrangement, the two phases may be separated. This operating principle is paricularly adapted to separate an oil/water emulsion into its two components. The axial outlet of this type of separator generally comprises a tubular part of low conicity which is connected to the cylindrical chamber by a conical part. A two-phase cyclone separator of this type is described in U.S. Pat. No. 4,749,490.
Also known are three-phase cyclone separators which are adapted to separate a solid phase, for example, sand, which is in suspension in an emulsion formed of, for example, oil and water. Such a three-phase separator is described in U.S. Pat. No. 5,332,500. In common with two-phase separators, three-phase cyclones have an outlet for one of the liquid phases which comprises an extended tubular part of low conicity.
One principal application for cyclone separators is the treatment of waste water from oil and/or gas production wells. Typically, cyclone separators are used on offshore oil production platforms to treat the oil/water/sand mixture which is separated from the production fluids in order to clean the water before its disposal or re-injection. Available space on a production platform is very limited. Several cyclone separators are generally installed side by side in a treatment unit located on the platform. However, the form of the previously described conical parts, and that of the tubular parts of low conicity, mean that there is a considerable amount of wasted space in the treatment unit between the various separators. Furthermore, it is desirable, in order to increase the efficiency of the separator, to provide a pre-treatment stage, upstream of the separator, for the mixture to be treated. In the case of an oil-water emulsion, this pre-treatment stage advantageously comprises a coalescer intended to transform the microscopic drops of oil in the emulsion into larger drops which are more easily separated in the cyclone. However, in the case where the treatment unit is to be installed on a production platform, such coalescers cannot be used due to the lack of available space.